TECHNICAL 12 · ANCHORS

Foundations and anchors: the cheapest part and the first to fail.

A greenhouse frame is held down by parts that cost a few percent of the order and decide whether it survives a storm. Ground screws, concrete-in, base plates: each suits a different ground and a different load.

Anchor types compared
Type	Ground	Uplift capacity	Removability	Cost
Ground screw 600–800 mm	Soil, no rock	Moderate	Removable	Low
Concrete-in leg	Any, needs curing	High	Permanent	Medium
Base plate + bolts	Concrete slab or pad	High	Permanent	Medium–high
Ballast block	Hard surface, no digging	Low–moderate	Removable	Low

Capacity depends on soil and depth, not on the type alone. Your engineer should size it.

What makes an anchor fail

Too shallow: the screw reaches loose soil, not bearing soil.
Soft ground after rain: capacity drops, and a storm arrives first.
Cement at the wrong mix: a 1:8 mix is not concrete.
No lateral restraint: the leg moves sideways and the frame racks.
Wrong bolt: a base plate with the right bolt but no anchor cage.

Movable structures

Berry growers relocate tunnels between blocks. That rules out concrete-in and points to ground screws or ballast. If movability is planned, it should be in the first quotation: the anchor type changes the frame detail, and retrofitting is expensive.

Frost depth

In cold markets the anchor has to reach below the frost line or the ground movement will lift it. Ask for the frost depth in the site brief; it is a number your local contractor will know.

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